Some well-known optical communications systems which transmit information through optical fibers use an optical switch of this kind.
If a trouble or fault takes place in such optical transmission line and disables the latter from transmitting further optical signals, the optical switch provided in this transmission system is used to put an auxiliary transmission line, if any, into service for further transmission of the optical signals. Such optical switches include one in which the construction is shown in FIG. 1(a). As seen, the optical switch comprises a stationary plug 101 having a connecting face A and to which one end of an optical tape core 100A consisting of a plurality of optical fibers laid parallel to one another is fixed; a moving plug 102 having a connecting face B. One end of an optical tape core 100B is connected to the plug 102, the tape core 100B also consisting a plurality of optical fibers laid parallel to one another. A connecting faces A and B abut each other. A driving mechanism 103 moves the moving plug 102 in a predetermined direction in relation to the stationary plug 101, thereby selectively connecting the optical transmission line (optical fibers in a group) in the optical tape core 100B to another optical transmission line (optical fibers in a group) in the optical tape core 100A; etc.
In the optical switching system having the above-mentioned construction, the optical switch is disposed anywhere, for example, in the middle of an optical transmission line made of an optical tape core in which plural optical fibers are laid parallel to one another. By operating the optical switch, the optical signals can be directed to any other destination or passed through any other optical transmission line. The optical switch operates on the principle described in the "Transaction of the IEEE, Vol. E73, No. 7 July 1990 pp. 1147-1149".
The construction of such optical switch will be described in further detail with reference to FIG. 1(a). As seen, the ends of optical tape cores 100A and 100B in pair are fixed to the stationary plug 101 and moving plug 102, respectively, made of a synthetic resin. Optical fibers opl, op2, . . . , op5 forming together each of the optical tape cores are equidistantly spaced from one another on one end face of each plug. Normally, the optical fibers exposed on the end face of the stationary plug 101 correspond one-to-one to those exposed on the end face of the moving plug 102 to transmit optical signals between the vis-a-vis optical fibers. For switching of the optical transmission line from one to another as in the above, the moving plug 102 is slid by the driving mechanism 103 in relation to the stationary plug 101, whereby the one-to-one correspondence between the optical fibers exposed on the end faces of the respective plugs is changed to switch the optical signal transmission route from one to another.
The mechanism of the above-mentioned optical switch will be further detailed herebelow. As forced by means of a push pin 104 disposed as a part of the driving mechanism 103, the face B' vis-a-vis to the connecting face B of the moving plug 102 slides in contact with a portion of the wall surface of a plug chamber 105a of a main body 105 in which the moving plug 102 is housed. When the moving plug 102 moves, however, a large frictional force develops between the moving plug 102 and plug chamber 105a so that the moving plug 102 cannot move smoothly.
FIG. 2 shows another example of the driving mechanism 103 in the optical switch of such structure. As seen, the driving mechanism 103 is provided with a solenoid (driving source) 106 which generates a magnetic force which will press a drive shaft 107 and the push pin 104 coupled with this shaft 107 by means of a coupling member 110, whereby the moving plug 102 which abuts the end face of the push pin 104 is moved in a predetermined direction.
For smooth sliding of the drive shaft 107 and push pin 104 within the main body 105 of the optical switch of this structure, it is necessary to insert the shaft 107 and pin 104 with their axes kept parallel to each other in the same plane. Namely, it is required that the center axes of the sliding holes in the main body 105, through which the shaft 107 and pin 104 are inserted, respectively, should be precisely parallel to each other in the same plane. In fact, however, some inaccuracy of the parallelism is unavoidable, so that the drive shaft 107 and push pin 104 slide with a wobble. In a worst case, the shaft and pin cannot slide.
In the above-mentioned optical switch, if the connecting faces of the plugs, where the latter abut each other, have any fine irregularities, the Fresnel reflection takes place to cause the efficiency of transmission to be reduced, which is an important problem.
In another example of the conventional optical switches, shown in FIG. 3, it has been proposed to charge as an matching agent an oil having a same index of refraction as the optical fiber in the plug chamber 108a in the main body 108 in which the plugs are housed, in order to prevent the Fresnel reflection from taking place even if the connecting faces have any fine irregularities. In this case, however, the oil is likely to leak from the clearance between the sliding hole wall and push pin, which is also a critical problem.
Normally in the optical switch shown in FIG. 4, each plug is placed in the plug chamber 108a of the main body 108 and the oil is charged in the plug chamber 108a, and when installing a lid in the concavity atop the main body 108 thereafter, the clearance between a lid 109 and the main body 08 is sealed with an adhesive to prevent the oil from leaking from that clearance.
In this optical switch, however, while the adhesive applied for sealing the clearance between the main body 108 and lid 109 is drying and solidifying, a portion of the adhesive flows into the plug chamber 108a of the main body 108 and mixes with the matching oil charged in the plug chamber 108a, causing the index of refraction of the oil to change.